Consider this: If a sizeable percentage of all North American over-the-road trucks could eliminate the need to idle for driver comfort entirely, there’d be nearly 4 billion gallons of diesel fuel saved every year.

And that figure doesn’t even include the thousands of hours idled away by dump trucks, city drivers or P&D guys. One year ago, the price of diesel was about 12 cents a liter less than it is now.

Idle your truck for more than three minutes in downtown Vancouver and you’re liable to be dinged with a $150 fine. Really, is there any math to be done?

In individual terms, eliminating idle time completely could save a one-truck operator $30,000 or more over five years. Still say an APU is too expensive?

It turns out, even one of the more elaborate models could return triple what you paid for it over five years — even more if they wind up on multiple trucks.

To achieve year-round idle-reduction capability, one needs an on-board source of power, primarily to run a cooling system. Cab and engine auxiliary heating systems have progressed to the point where they are as compact and efficient as they can be, but that leaves the summer months to consider. Battery powered A/C systems are emerging, but they’re expensive, and not quite as effective, yet, as a full air conditioning system.

Enter the genset or auxiliary power system (APU). They aren’t the same thing, for the record, but one or the other may be a better solution for your personal needs.

Both consume a fraction of the fuel required to run the truck’s big diesel –by a factor of about 8:1, but a genset (generator) is simply a diesel-engine powered source of 110-volt AC power — which can be used to run appliances like fridges, microwaves, etc., and remote heater and/or air conditioning systems.

An APU, on the other hand, uses a small diesel engine to produce DC power to run built-in climate-control systems. Coolant from the APU engine can be used to heat the big diesel in the winter for reliable cold starts, and depending on the level of integration, some APUs have their own A/C compressors but use the truck’s A/C condenser for cooling. Most of the DC systems onboard the truck can be used as usual — with an inverter –while a DC alternator on the APU engine keeps the main batteries charged.

In accordance with the EPA’s new emissions guidelines, come 2008, APUs will require diesel particulate traps, similar to the ones coming our way on 2007-model trucks. Though, according to Ed O’Malley, vice president of dealer development at Blackrock Systems, a maker of the integrated variety, “the smaller diesels will not come under serious environmental regulation until 2017.”

And at least one APU manufacturer has declared its product ULSD compliant. RigMaster has announced that all its current models will operate on the ultra low sulfur diesel.

APUs come in many guises but in just two configurations: integrated –meaning they have their own AC compressor and condenser and heat exchanger and don’t need to tie into the truck’s system; and non-integrated-meaning they use the truck’s HVAC system and circulate coolant from the APU to provide heat while running an A/C compressor, but use the truck’s condenser and air circulation fans.

The integrated APUs usually include an under-bunk unit housing the A/C and the heat exchangers, as well as the fans and ductwork.

In accordance with the EPA’s new emission rules, APUs
will also require diesel particulate traps starting in 2008.

Blackrock’s O’Malley says there can be warranty and reliability issues when breaching an OEM’s A/C circuit, for example. “When you have multiple hoses and connectors, you increase the potential for leaks,” he says. “And when you tap into the cooling circuit, you’re adding more hose again, and a coolant leak can take the whole truck down.”

Some of the non-integrated units, such as Carrier’s ComfortPro (formerly known as Proheat), use a 120-V AC generator to power an electric-drive A/C compressor, mounted under the sleeper. These non-integrated units offer some flexibility in the mounting positions of both the external and internal components.

And we’re not done with variety just yet. The Willis APU, manufactured by Auxiliary Power Dynamics LLC, can be ordered with an integrated air compressor to maintain system air pressure on the truck, and a heavy-duty alternator capable of supplying power to the truck’s electrical system.

“APUs with heavy-duty truck components, like alternators, can better handle the high power demands and the high operating temperatures of a Class 8 truck diesel engine,” says Will Watson, vice president of sales and marketing for Auxiliary Power Dynamics. “Plus, they can act as backup for their counterparts in the truck engine.”

Also entering into the APU game is one of the world’s biggest manufacturers of kitchen and bathroom products — Kohler. Kohler’s 5-kw non-integrated APU is unique in that it’s air-cooled and designed with a direct-drive alternator — a direct connection between the engine and alternator.

If you’re worried about added weight you might want to look at Idle-Kleen’s efficient Hitchhiker, a non-integrated unit that adds only about 220 lb to your vehicle. The Cambridge, Ont., based manufacturer also say that the Hitchhiker can be installed easily, in just a few hours.

Kelly Cooper of Idle-Kleen says that the recent fuel spikes have been commensurate with unpredicted spikes in sales. “We thought we’d be doing three to 500 units a year and it’s more like three to 5,000.” The Hitchhiker retails for $6,950.

The OEMs have also experimented with various technologies to provide on-board sources of heating, cooling and power.

Kenworth’s “Clean Power” system provides up to 10 hours of cooling capacity, used in conjunction with a set of deep-cycle batteries to power fans, as well as electric heat in the cooler months. Peterbilt offers a similar system, called the Comfort Class system. Both work with shorepower systems.

Freightliner’s NITE (No-Idle Thermal Environment) by Bergstrom, consists of a rechargeable battery bank that supplies power to a 3,500 BTU AC system and an auxiliary heater. It provides up to 10 hours of cooling capacity.

And International’s No Idle APU allows drivers to operate heating or air conditioning, as well as “hotel loads,” such as a microwave or television, without running the engine of the truck. It offers 6kW, 120-volt AC power; plus 50 Amp, 12-volt battery charging; and provides 10,000 BTUs an hour of air conditioning or heat.

APU makers offer a variety of system capacities. Cooling system capacities, for instance, can range from 10,000 to 26,000 BTU. Quite a spread, but one system may be designed to cool a large sleeper and the cab, while the other may be intended just for the sleeper. Buy as much capacity as you can without over-buying.

The same goes for AC and DC electric production. If you plan to run a TV, an air conditioner, a microwave, and a hairdryer all at the same time, you may need a larger generator or alternator. If your power needs are more modest, you may save a few dollars spec’ing a lighter unit.

An auxiliary system should accomplish three things: provide a power source for driver convenience, and provide heating and cooling capabilities for driver comfort. The means vary across the brands, but the end result is the same.